Background and aim of the study: The effect of left ventricular (LV) pressure overload on right ventricular (RV) diastolic function has been extensively studied. In-contrast, no data are available concerning the influence of LV volume overload on RV diastolic function. Accordingly, RV diastolic function was studied in patients with mitral regurgitation (MR) using Doppler echocardiography. Methods: RV diastolic indices were calculated, using pulsed Doppler echocardiography, in 30 patients (mean age 56.87 +/- 8.58 years) with severe MR, and in 30 healthy control subjects (mean age 56.67 +/- 8.52 years). Results: Compared with controls, MR patients had a significantly lower RV E/A ratio (0.85 +/- 0.12 versus 1.21 +/- 0.16, p < 0.001), a significantly prolonged RV isovolumic relaxation time (70 +/- 20 versus 30 +/- 10 ms, p < 0.001), a significantly prolonged deceleration time of the transtricuspid E wave (210 +/- 20 versus 140 +/- 10 ms, p < 0.001), and a significantly greater right atrial filling fraction (38.58 +/- 4.59 versus 32.58 +/- 3.14%, p < 0.001). There was no statistically significant correlation between RV diastolic indices and IV mass index and interventricular septum thickness. Conclusion: RV diastolic function in patients with MR is impaired, reflecting prolonged relaxation and redistribution of RV filling into late diastole. Ventricular interdependence constitutes the most likely mechanism of this action.